This invention relates to a device for moving workpieces to predetermined positions with respect to an industrial robot for automated manufacturing operations.
This invention specifically improves upon the traditional positioner design currently employed by those in the prior art. A typical workpiece positioner includes an H-shaped frame structure having a plurality of fixture supports. These devices are generally known as "exchange-axis positioners", "three-axis tables" or "Ferris-wheel positioners". The Ferris-wheel positioner and the three-axis table are the two most typical styles currently used.
As shown in U.S. Pat. Nos. 5,074,741 and 4,666,363, issued to Johansson, the traditional Ferris-wheel table operates about three axes. The workpieces are supported between the legs of the H-shaped frame structure and can be rotated around two independent horizontal axes. The H-shaped frame structure itself rotates about a similar horizontal axis. The three-axis table also rotates the workpieces about horizontal axes, and rotates the H-shaped frame structure about a vertical axis generally perpendicular to the plane of the H-shaped structure.
Several problems with these traditional types of positioners occur when workpieces sizes approach the maximum work envelope of most industrial robots. For example, in the Ferris-wheel positioner, floor clearance determines the maximum size of the workpiece that can be turned. As the workpiece gets larger, more floor clearance is required to allow the bigger piece to turn about the horizontal axis which runs axially along the H-shaped frame structure. As floor clearance gets larger, the center line of rotation, or third axis (exchange axis), gets higher and, resultantly, puts the station load height, or robot operation height, or both, inconveniently high.
In the three-axis table positioners, robot clearance is required to allow the positioner to turn about its vertical axis. As the workpiece gets larger, more robot clearance and distance from the table is required to allow the bigger piece to turn. As robot clearance increases, the proximity of the robot to the ultimate position of the workpiece is compromised. This imposes the additional requirement that the robot must either be moved during the turning of the positioner or forego optimum reach on the workpiece.
In both positioner styles, the speed of the axis exchange must always be compromised as part sizes and weights go up. This is because of the extreme distance of each workpiece axis from the center line of exchange axis or rotation.